Drainage of Roads & Tunnels

Infrastructure drainage is the collection and drainage of surface water from roads, motorways, railway stations and tunnels. Aspects of water management, soil and nature conservation and, depending on the case, also landscape conservation and urban development play a role.

In tunnel drainage, the fire behaviour of the materials used is particularly decisive in order to be able to meet required fire protection regulations.

Drainage of Roads & Motorways

Many criteria must be taken into account for roadway drainage. Influencing factors include the conditions of the road with the possible water run-off, the use of the road and various guidelines such as ZTV Ew-StB 14 (Additional Technical Contract Conditions and Guidelines for the Construction of Drainage Facilities in Road Construction). Local standards may differ.

At the same time, both load requirements and hydraulic capacity must be taken into account. In addition, the drainage system must be adapted to the type of pavement already during the planning stage. This is because each type of pavement has its own challenges. For example, drainage systems for porous asphalt layers (polymer-modified asphalt) must allow for a second drainage level.

What Happens to the Rainwater?

Rainwater management for roads is not only the drainage of rainwater. In general, a distinction is made for roads as to whether the rainwater infiltrates on site or is discharged into a receiving watercourse.

What to consider for on-site infiltration
- Soil properties, in particular the permeability of the soil
- Distance to the groundwater
- Local conditions of the road, e.g. special rules apply in water protection areas
Restrictions on discharge into surface waters
Emission and immission requirements are decisive here. This means that provisions must be observed that regulate which waters may be discharged into and which must be protected from discharge. Here, too, strict rules apply to water protection areas.

In addition, the location of the drainage systems in relation to the receiving water, i.e. the water runoff, must be taken into account in advance in the planning of motorway and road drainage. How far away is the receiving water? At what elevation can drainage take place? Is a lifting station required due to the height level?

Cleaning of the Rainwater

No matter which type of drainage is chosen, in any case it is necessary to clean the water runoff. The rainwater itself is not harmful, but pollutants are washed off the roads. These can be, for example, oil spilled on the road by an accident or microplastic particles from tyre wear. These must be effectively retained – for example, by means of surface filtration.

Multiple drainage channels along the motorway — Pollutants can easily collect in drainage channels along the motorway, making the rainwater polluted.

Further Requirements & Trends from the Field

Trafficability:: Drainage channels must be at least class D 400 due to the traffic of cars and lorries. In motorway construction and on motorway-like roads, there is a trend towards higher classes, E 600 and even F 900. This is because during the rehabilitation of a motorway, drainage channels located along the road may also be driven over when traffic is temporarily diverted.
Durability:: Drainage channels must be resistant to frost and de-icing salt.
Safety:: With the correct installation of the drainage channel and grating, a high level of safety is achieved. The choice of the right type of grating (in relation to the type of traffic) can also reduce the noise level during passage.

Function

For some platforms, there may be restrictions on the construction height. Linear drainage systems in a flat design are therefore ideally suited to absorbing and quickly draining precipitation water. Platforms are often designed for a large number of passengers. The areas that connect to the drainage systems are therefore large and usually completely sealed. The amount of precipitation must be safely collected and drained. In addition, the construction materials used – including drainage channels – should be non-conductive. This requirement applies specifically to the protection of passengers. In the event of an accident, current-carrying overhead lines should not become a hazard for people on the platform.

Tunnel Drainage

A major challenge in tunnel construction and the drainage installed there is fire protection. There are also some special features for the planning.

Drainage channel along the road and in a tunnel

Fire Protection & Special Guidelines

There are two standards that evaluate building materials according to their combustibility and flammability. In Germany, DIN 4102 applies to the fire behaviour of building materials and components. Throughout Europe, DIN EN 13501 is used.

DIN 4102 – Fire Protection Classification
DIN 4102 – 1 classifies building materials as non-combustible (A1, A2) or combustible (B1 – B3).

In tunnel and emergency exits, all materials must comply with the highest fire protection class (DIN 4102, A). A1 applies to non-combustible building materials that do not contain any combustible components, do not develop smoke or prevent burning droplets (e.g. concrete). A2 designates non-combustible building materials that may, however, contain certain proportions of combustible substances and materials. With regard to smoke development and dripping, the same guidelines apply as for A1.

The RABT (Guidelines for the Equipment and Operation of Road Tunnels) and the ZTV-ING (Additional Technical Contract Conditions and Guidelines for Engineering Structures) apply specifically to tunnel construction. The regulations also include the Guideline Drawings for Engineering Structures (RiZ-ING).

Planning Challenges

In an early planning phase, slope situations must be taken into account and planned.

The longitudinal or transverse gradient of the road as well as the gradient course (elevation of the road axis) are decisive here. In addition, the elevation of the receiving water is important, because if the tunnel drainage is lower than e.g. streams or canal systems, lifting systems are necessary.

For permanently reliable drainage, requirements for resistance (frost, de-icing salt, etc.) must be taken into account, as well as the exposure of the concrete quality of drainage channels and their foundations. For concrete drainage channels, the exposure classes XC4, XD3, XF4 apply.

How do you find the right drainage solution for your infrastructure project?

Drainage channel in the tunnel in Krakow

Our engineers deal with detailed questions on the drainage of roads, motorways, railway stations and tunnels on a daily basis. Put your trust in our experience!

For water cleansing, our experts recommend the use of DRAINFIX CLEAN. The filter channel system reliably protects the environment from harmful influences that can enter water bodies through runoff water from roads and motorways.

Learn more about sustainable rainwater treatment

Product illustration of a FASERIX SUPER drainage system

The concrete used to make the FASERFIX drainage channels meets the requirements of DIN 4102 and is classified as A1 (non-combustible). In the event of a fire, HAURATON concrete drainage channels therefore offer maximum safety and can contain or prevent the spread of fires.

Our FASERFIX drainage channels are also: